The conversion of acetoacetyl-CoA to acetoacetate (FIG. 1) is an essential step in metabolic pathways with such intermediates. The specific hydrolysis of the thioester bond between coenzyme A (a thiol) and acetoacetate (an acyl group carrier) in acetoacetyl-CoA is an efficient way to produce the aforementioned conversion. Two classes of naturally occurring enzymes have been used to mediate such conversion including, CoA transferases (E.C. 2.8.3.-) and CoA-hydrolases (thioesterases) (E.C. 3.1.2.-). However, while acetoacetate-CoA transferases require the presence of a non-activated acid acting as CoA acceptor, the CoA-hydrolases (acyl-CoA thioesterases) described to act on acetoacetyl-CoA are unspecific in the sense that they react with the same order of magnitude with acetyl-CoA, the substrate required for acetoacetyl-CoA formation by the enzyme thiolase (E.C. 2.3.1.9), thereby degrading the substrate for the acetoacetyl-CoA biosynthesis itself.
Therefore, there exists a need in the art for improved enzymes to mediate the conversion of acetoacetyl-CoA to acetoacetate.